Morphological plasticity allows coral to actively overgrow the aggressive sponge Terpios hoshinota (Mauritius, Southwestern Indian Ocean)

Terpios hoshinota is a threat to coral reefs. It is an encrusting sponge that kills scleractinian corals by overgrowing them. Predominantly reported from the Indo-Pacific region, the sponge seems to be progressively expanding its range by moving towards the western Indian Ocean. It is still unclear what causes its outbreaks. We report for the first time its presence at our study site at the southwestern Indian Ocean island of Mauritius (20°10′S, 57°31′E). Our surveys showed that T. hoshinota could grow linearly by 11.5 ± 3.60 mm month −1 . In 2014, T. hoshinota had covered 11 % out of 500 m 2 of available hard substrate. We also report a rare encounter with Montipora aequituberculata, a scleractinian coral species that was able successfully to overgrow established sponge colonies. The sponge colonies did not react to the overgrowth by putting out tendrils and made no attempt to cover the Montipora aequituberculata . The coral was able to overgrow T. hoshinota because it did not directly attack the growing front of the sponge. The high growth rate and high plasticity of M. aequituberculata helped the coral to overgrow and take the space of the sponge.